EMAIL INBOX MESSAGES DISSAPEAR

I installed Sage ACT! Premium 2012 Version 14.0.572.0, Hot Fix 2, and sometimes when I check and send mails in the Inbox of some accounts mails dissapear and new mails download in the inbox (they are mails that are in the internet server.

How do I do to restore the dissapeared mails? How do I resolve this problem?